Neuronal cell death in the developing nervous system probably results from activation of an endogenous "death program". There is considerable interest in identifying cell death genes in vertebrates; however, at present none have been isolated. An in vitro model system has been developed to characterize cellular and molecular events in neuronal cell death. It consists of a subline of PC12 cells that undergoes RNA and protein synthesis-dependent cell death following removal of NGF. Using this model system, 6 cDNAs have been isolated that are un-regulated in dying cells. Characterizing these cDNAs and identifying additional genes activated in dying cells is the major focus of the proposed studies. This information should improve our understanding of mechanisms responsible for neuronal cell death. The long term goal of these studies is to understand cellular and molecular mechanisms involved in neuronal cell death with the hope of identifying ways of blocking cell death following trauma or in neurodegenerative diseases. The Specific Aim of the proposal are: 1) to use biochemical, molecular and immunological techniques to characterize the 6 cDNAs already isolated from dying cells, 2) to determine if modulating levels of their proteins affects cell survival and/or cellular processes, and 3) to identify low abundance, possibly regulatory genes, induced at early times after removing NGF by making and screening a subtracted cDNA library. Understanding why and how neurons die should have a tremendous impact on both basic and clinical neuroscience. It is obvious that the present study can not address the large number of questions dealing with why neurons die during development, aging, trauma, or neurodegenerative diseases; however, the proposed experiments represent an initial endeavor to identify biochemical and molecular events responsible for neurons dying following loss of trophic support. A fundamental knowledge of genes that control cell death and the molecular cascade of events resulting in neuronal cell death is important for understanding a variety of developmental events as well as providing potentially important information for pathophysiologies associated with the normal aging process or neurodegenerative diseases.